This invention relates to reactive adducts of certain vinyldioxo compounds and to curable coating compositions comprising such reactive adducts.
Vinyldioxo compounds also referred to herein as VDO compounds) are well known and certain members of the class have been disclosed as polyester curing agents in U.S. Pat. No. 3,291,860. All are cyclic acetals, extensively studied and patented by Ikeda (U.S. Pat. Nos. 3,010,918; 3,010,923; 3,197,484), by Brachman (U.S. Pat. No. 3,014,924), and by others and described in detail by Hochberg (JOCCA 48, 11, 1043-1068, 1965). The simplest compounds in this class are made by a reaction of acrolein with a compound having two hydroxyl groups, either on adjacent carbon atoms or on carbon atoms separated by an additional carbon atom. When more than two hydroxyl groups are present in a compound, different pairs of hydroxyl groups can react with the aldehyde to form a cyclic acetal. Typical compounds having at least two hydroxyl groups include, for example, ethylene glycol, glycerin, 1,2,6-hexanetriol, and trimethylolpropane. Depending on the number and type of hydroxyl groups, the resulting VDO can be either a substituted 1,3-dioxolane or a substituted 1,3- dioxane, but frequently it is a mixture of a dioxolane with a dioxane. The reaction of acrolein (1) with trimethylolpropane (2) is shown below in Equation 1. The formation of VDO compounds, like other acetal-forming reactions, is catalyzed by acids. ##STR1##
The reaction product according to formula (3) is a 2-vinyl-1,3-dioxane substituted with an ethyl group in the 4-position and with a hydroxymethyl (methylol) group in the 6-position. Analogous reactions can be used to prepare substituted rings having four to ten carbon ring members, that is, substituted dioxirane, dioxetane, dioxolane, dioxane, dioxepane, dioxocane, dioxonane, and dioxecane.
VDO compounds and their various derivatives have been described as useful polymerizable materials, which have the potential of providing both pigmented and clear-coat finishes in automotive and other applications. Those compounds polymerize in the presence of oxygen, such reactions being catalyzed by cobalt compounds. In an aqueous medium and in the presence of acids, the VDO compounds are unstable, so that further reactions are carried out in either a neutral, alkaline, or organic medium. Hochberg (op. cit.) discusses various syntheses and properties of many VDO compounds. In spite of the great industrial potential of VDO compounds, they have not been successfully commercialized in high performance coatings.
It has recently been found that VDO compounds can be polymerized, with ring opening, in the presence of an acid, as described in WO95/19975. For example, one of several reactions that may take place involves the above compound of formula (3) in the following equation 2: ##STR2##
The hydroxyl group of the polymer attached to the repeating group in formula (4) can be used for crosslinking by reaction with a difunctional or polyfunctional compound to form a solid coating. This is done starting with a liquid component or with two liquid components, in the absence of a solvent or with a minimum amount of a solvent or diluent.